Combined motor and voltmeter

ABSTRACT

A voltmeter associated with a motor is operated by the magnetic field produced by the motor. A metal sensitizing element which is adjustable controls the sensitivity of the meter to the field.

O United States Patent 1151 3,662,265 Besancenot 1 May 9, 197 2 541 COMBINED MOTOR AND VOLTMETER 2,998,571 8/1961 Corson et al ..324/147 [72] Inventor: serge Besancenot 5 rue Edouard 2,183,566 12/1939 Hoare ..324/l47 vestre, Sevran (Se1ne-St.-Den1s), France FOREIGN PATENTS OR APPLICATIONS [22] 1969 5,440 3/1908 Great Britain ..318/490 [2]] Appl. No.: 875,181

Primary E.\'aminer-Alfred E. Smith 52 U s. (:1 ..324/157, 324 147 324/158 MG Schwartz Nisse [51] Int. Cl ..G0lr 1/20 58 Field of Search ..324/147, 157, 158 MG; 318/490 1 ABSTRACT A voltmeter associated with a motor is operated by the mag- [5 6] References cued netic field produced by the motor. A metal sensitizing element UNITED STATES PATENTS which is adjustable controls the sensitivity of the meter to the field. l,50l,l89 7/1924 Record ..324/l47 2,825,871 3/1958 Evans ..324/i58 MG 1 Claim, 6Drawing Figures COMBINED MOTOR AND VOLTMETER This invention relates generally to electrical devices and to means for monitoring the voltage supplied thereto, for the purpose of maintaining the voltage constant.

One example of such a device is the motor of an automatic transparency projector, which motor controls the feed of a slide holder and the forward and return movement of each transparency with respect to the beam of light from a lamp and an optical system. An appliance of this type therefore comprises at least one motor and a lamp which must be supplied from the mains at different voltages, each of which must be constant.

This effect can be achieved of course by means of an autotransformer comprising a primary winding fed from the mains and having appropriately distributed tappings to give the required fractions of the mains voltage, each fraction being adapted to the appropriate element of the appliance. Thus when the voltage supply is 220 volts, a first pair of tappings will give a voltage of 120 volts suitable for the motor supply, while other pairs or a secondary winding will give voltages of 12 volts suitable for the projection lamp supply.

In actual fact the latter voltage is the one that is required to be kept constant in order to maintain the brightness of the projected picture while protecting the lamp filament. To this end it is conventional practice to dispose a rheostat which is controlled by a contactor in one of the supply leads to the transformer primary winding, and to check any variations with a voltmeter which is mounted in the lamp supply circuit.

The results of this type of circuit are as follows: firstly, operation of the rheostat will not only affect the lamp supply but also the motor supply; secondly, and conversely, operation or stoppage of the motor will affect the lamp supply; finally, the fact that the motor and voltmeter winding are situated near the appliance will cause misadjustment of the voltmeter. An attempt has been made to overcome this by means of a metal member acting as a shunt, adjustment of which allows resetting of the voltmeter zero.

The invention makes use of these features to provide a considerable simplification of such appliances based on the use of the magnetic field of the motor to replace the voltmeter winding field and hence completely eliminate this winding.

The invention relates to the combination of an electrical device having a coil to which, during operation, a voltage is applied producing a magnetic field and a voltmeter for monitoring the voltage supplied to the coil wherein the voltmeter comprises a movable member responsive to a magnetic field produced by a coil when a voltage is applied thereto, characterized in that the coils are common.

In a preferred embodiment the electrical device is the motor of a transparency projector.

It is in fact well known that such projectors are designed to be as compact as possible so that their components are very close to one another and it is also known that the common supply circuit to the projector lamp and motor is provided with a voltmeter and a rheostat is provided to adjust the voltage to the optimum value to provide optimum projection brightness without overloading the lamp.

One embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawing, wherein:

FIG. 1 is a partially broken-away perspective view of a conventional voltmeter;

FIG. 2 is a similar view of the voltmeter according to the invention;

FIG. 3 is a top plan view of the voltmeter of FIG. 2;

FIG. 4 is a perspective view of the metal strip for calibration of the voltmeter of FIG. 2;

FIG. 5 is a top plan view of the strip of FIG. 4; and

FIG. 6 is a side view of the strip of FIG. 4.

Referring to the drawings, the moving system of the voltmeter comprises a needle 1 moving with respect to a graduated scale 2 and borne with a spindle 3 rotating against the force of a spiral spring 4. The spindle bears a metal plate 5 disposed in a lane passing throu h the spindle 3.

n the convention voltmeter shown in FIG. 1, this system is mounted at the center of a winding 6 carrying the current supplied to the instrument, and a soft iron strip 7 of triangular profile is disposed around the inside, the shortest side 8 of the triangle being situated opposite the plate 5.

The operation of this conventional voltmeter is as follows: as soon as the winding 6 carries a current it produces a magnetic field so that the two metal components 5 and 7 are charged to repel one another. The strength of the field is proportional to the current so that the repulsion force and hence the angle of deflection of the needle are an indication of the voltage supplied. I

In the voltmeter shown in FIGS. 2 and 3, for monitoring the voltage applied to a motor M, the stationary members 6 and 7 are eliminated and the moving system l35 is disposed directly in the magnetic field produced by the motor M itself. The metal plate 5 is subjected to the action of this magnetic field and is deflected proportionally to said field and hence to the current passing through the motor.

In practice, to make the system more sensitive, the magnetic field of the motor M is distorted by a metal member 9 secured to the motor casing. The shape of this member 9 determines the relationship between angular movement of the plate 5 and the voltage applied to the motor; for a linear relationship the member should have the profile shown in FIG. 2.

To calibrate the voltmeter, i.e. set its zero point all that is necessary is to move the member 9 with respect to the plate 5.

FIGS. 4 to 6 show the most advantageous shape and construction of said member 9, which have been determined from exhaustive experiments.

From these Figures it will be seen that the member is made of two parts (a-b-c) and (f-g-h-i) pivotably connected about a rivet e. The portion (a-b-c) is in the form of an angle member, one side a of which is bent over to form a lug c having an aperture at d for fixing an adjustment on the motor casing.

The portion (f-g-h-i) comprises extensions in three perpendicular planes and by being pivotally secured adjacent the end of the side b of the first portion can affect the motor field so as to distort it in any direction. Once the calibration has been carried out, the two portions of the member 9 are secured so as to retain the final zero setting.

What we claim is:

1. In combination with a motor adapted to produce a magnetic field, a meter comprising first means magnetically coupled to and, sensitive to said magnetic field to produce a reading, and second means in said magnetic field for adjustably varying the magnetic coupling of the motor and first means, said second means including a metal part mounted on the motor and positioned in part between the motor and first means, said metal part including pivotably connected sections, one of which includes connected elements in three mutually perpendicular planes. 

1. In combination with a motor adapted to produce a magnetic field, a meter comprising first means magnetically coupled to and, sensitive to said magnetic field to produce a reading, and second means in said magnetic field for adjustably varying the magnetic coupling of the motor and first means, said second means including a metal part mounted on the motor and positioned in part between the motor and first means, said metal part including pivotably connected sections, one of which includes connected elements in three mutually perpendicular planes. 